Saw-tooth wave generator circuit arrangement



Oct- 14, 1941- D. J. FEWINGs ETAL 2,258,752

SAW-.TOOTH WAVE GENERATOR CIRCUIT ARRANGEMENT Filed 001'.. 3, 1939 3 SheeLs-Shee'l 1 upd ATTORNEY 06t- 14, l941- D. .1. FEWINGS ET AL 2,258,752

SAWFTOOTH NAVE GENERATOR CIRCUIT ARRANGEMENT Filed Oct. 3, 1939 5 Sheets-Sheet 2 fhade Rag Tube /a 2lb INVENTORS D- J. FEW/NGS E J. KEMP ATTORN EY Oct. 14, 1941. D.. 1. FEWINGS ET AL 2,258,752

v SAW-TOOTH NAVE GENERATOR CIRCUIT ARRANGEMENT Filed oct. 5l 1959 5 sheets-sheet 5 Caf/10d? Pay Tube INVENTORS D.J FEW/NGS BYR-J. KEMP Patented Oct. 14, 1941 `SAW-IO'ITl-I WAVE GENERATOR CIRCUIT ARRANGEMENT David'John Fewin'gs and Roland John 'Kemp Chelmsford, England, assignors. to Radio Corporation of America, a corporationof Delaware Application October 3, 1939, .Serial No.. 297,658

v In Great Britain October 6, 1938 (Cl. Z50-36) 3r Claims.

This invention relates' to saw' tooth waver generator circuit arrangements'andl has for its object to provide improved circuitV arrangements capable of giving a powerful saw tooth wave output of good wave form and high frequency suitable for use for cathode ray deflection in` high fidelity television systems.

Difficulties are encountered in known saw tooth wave generator circuit arrangements in obtaining saw'tooth wavesv of large amplitude and good Wave form at high frequency. For example at operating frequencies o f l K. C.

. per secondand more, the amplifier normally provided in known arrangements for the originally genera-ted wave (this amplifier is usually a para- 1 phase amplifier having. an input saw tooth voltage wave-of small amplitude and intended to' provide amplied Waves of opposite instantaneous polarity for application to the deection plates of` a'cathode ray tube). tends seriously to round off what should be the sharp top of the wave, while it is very difcult to preserve a fast fly back, i. e., a short steep formation to the shorter flank of the saw tooth.

According to this invention a saw tooth wave generator arrangement comprises means for generating a sequence ofl short uni-directional, im-

pulses, ay pair of condensers, means .for charging said condensers each at, the same predetermined rate,fand means actuated by said impulses for alternately discharging said condensers at equal intervals whereby voltage saw tooth waves .in

former 2 (this is shown in `Figure 1 asan rauto"- transformer) the mid-point of which is'conf nected to the cathode of valve l. One end. of

the secondary of transformer 3 is connected through a condenser 4a to the cathoder of. a diode 5a and to a tap 6a on a potentiometer 'I. The other end of the secondary of transformer 3 is connected` through a condenser 4b to the anode of a diode 5b and vto a .point 6b on the potentiometer l. The anode of diode 5a is connected to. the earth point and to the center point 8 of the potentiometer through a condenser 9a while the cathode of diode 5b is connected to earth andv toV point 8 through condenser 9b. A source of high poten.

tial is connected across the Vpotentiometer .'I., the positive terminal -being at 'It and the negative at I I. The positive terminal I0 is connected. to

the anode of diode 5a through a resistance-ma y while the negative terminal II .is `connected to the cathode of diode 5b through a resistance IZb. A resistance I3 is connected between ter minals I0 and II and anode and screen grid potentials for the valve I (shown as a screen grid phase opposition are yset up across said condensers. Preferably the voltage wave across` each condenser is applied to a separate single/stage amplifier for amplification thereby the 'anode circuits of the two ampliers being coupled one toy one and the other to the other of a pair ,of cathode ray tube deflection plates.

The invention is illustrated in Figures 1, 2 and 3 of the drawings which show diagrammatically three embodiments thereof.

Referring to Figure 1, 'a valve I is connected by meansincluding a transformer 2 4in a known vso-called blocking oscillator circuit so that it "provides a series of short uni-directional impulses of small amplitude. 'I'he output circuit of this valve includes the primary of a transformer 3 andv it will be seen that the uni-directionall im- 'pulses at the -1 control gridof the valve I will appear atthe center tapped secondary winding of the transformer 3 as pulses with maximum voltage peaks of opposite polarites. The midpoint of the secondary of transfornfierV 3 is eartlied and connected to one end of the transvalve) are applied from the intermediate point I4 on said resistance I3. Thefju'nction point of elements 9a Iza is coupled through condenser Ia to the grid of a valve Ita, and the` junction point of elements 9b and I2b is coupled through condenser |511 to the grid, of a valve Ib'. The anodes of these two valvesV Ita lebV are respec tively coupled through condensers Ila, I'Ib` to the plates ,Ita |811 of -a pair of deflector plates of a cathode ray tube, a resistance I9 with an earthed center point 20 being provided between these plates. A similar circuit arrangement (not i shown) and operating at the` appropriate de' sired frequency may beprovided for the other pair of plates Zia, 2lb. v j

In this arrangement the' elements with the sufIiX a are in the circuit. which is triggered`r by impulses of one polarity and the elements with the suffix b are in the. circuit which is triggered by impulses of the vother polarity.. Thus the diode 5a is biased to mit off, and, in jthe static condition therefore, the condenser Ga is charged positively from point It through the resistance [2a which is of highA value. When condenser 4a passes a negative. impulse the normal bias on diode 5a is overcome and the diode.v

becomes conductive offering a rapid y.lischarge path across condenser 9a. In this way arsaw. tooth wave is built up acrosscondenser 9a this is amplified byy valve. Ita and applied `to plate ISG. The elements 41?; 5b, 9b, and 12h function similarly to elements 4G, 5a, Sa and 12a except, as will be obvious from this figure, that the condenser 9b receives normally a negative charge through high resistance |211 and is discharged through dode 5b when a positive iinpulse is passed by condenser 4b. Thus the saw tooth voltage wave which appears across condenser 9b and is amplied by valve Ib and applied to plate 18D is in phase opposition to that applied to plate |811.

The embodiment shown in Figure 2 is very similar to that shown in Figure 1 but. the transformer 3 of Figure 1 is dispensed with and instead, the valve I is resistance-capacity coupled by elements 22, 23, to an additional valve 24, the anode of which is connected to the pointr and the cathode of which is earthed through a selfbias resistance-capacity combination 25.. The elements 22, 23 are chosen to give a time constant such that the voltage impulses appearing at the anode of valve 24 consist of positive pulses each immediately followed by a negative pulse, both pulses being equal about the zero axis. A separate source (not shown) of anode voltage is provided for the valve 24, the positive terminal thereof being connected at 2E.

In Figure 2 the condensers 9a and 9b are charged linearly through the resistances l 2a and I2b, the condenser 9a accumulating a positive charge with respect to ground, while the condenser Sb accumulates a negative charge with respect to ground. Connected between the ungrounded electrode of each of the condensers 9a and 9b and a point along resistance 1 is a diode, the diode being so biased that it is rendered nonconductive even with the condensers charged until a triggering impulse is supplied by the tube 24. As shown in Figure 2, voltage variations of short duration and of positive polarity are present at the anodel of tube 24, these voltage variations being immediately followed by short impulses or voltage variations in a negative direction. The short positive pulses initiate conductivity in tube 5b while the short impulses of negative polarity initiate conductivity in tube 5a. These two diodes, therefore, substantially instantaneously discharge the condensers 9a and 9U, in order that they may again be charged through the resistances l2a and |2b. Amplifier tubes Ilia and Ib are provided for amplifying the intensity of the voltage variations derived from the ungrounded electrode of the condensers, and the outputs of tubes IEa and I6?) are combined and impressed upon the deflecting means for the cathode ray tube.

In the modification shown in Figure 3 the blocking oscillator valve l is resistance-capacity coupled by elements 22', 23 to the grid of a valve 21, the necessary phase reversal action being obtained by accommodating the saw tooth wave generating charge and discharge circuits (incorporating the condensers 8a and 9b) respectively on the anode and cathode side of the valve 21. The circuit of Figure 3 is suitable for use in cases where the saw tooth waves required to appear at plates I8a and I8b are of moderate amplitude. Figure 3 is shown with the transformer 2 of the blocking oscillator being a two-winding transformer instead of an autotransformer.

In Figure 3 the condensers Sa and 9b are charged linearly through the resistances I2a and |217, one electrode of each of the`condensers being connected to ground. A discharge tube 21 having a cathode, a control electrode and an anode, is provided, with the cathode connected to the ungrounded electrode of one of the condensers and with the anode connected to the ungrounded electrode of the other condenser. 'I'he tube 21 is normally non-conductive, but is rendered conductive by impulses derived from the blocking oscillator tube l. When the impulses from the blocking oscillator are applied to the control electrode of tube 21, the tube is rendered conductive and the condensers 9a and 9bare substantially instantaneously discharged. The voltage variations which are derived from the ungrounded electrode of each of the condensers are amplified by tubes 16a and IGZ), in order to increase their amplitude and the voltage varia tions after amplification are then combined and applied to the deecting means of the cathode ray tube.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed we declare that what we claim is:

l. A system for producing complementary potential variations of saw tooth wave form comprising means for producing a series of negative impulses of a predetermined'frequency and for simultaneously producing a series of positive impulses of the same frequency and substantially in phase therewith, a rst and a second condenser, means for charging said condensersv at opposite polarities and at a substantially uniform rate, a first and a second diode, means for effectively connecting the said first and second diodes in parallel with the said first and second condensers, means for applying the produced negative and positive series of impulses to the cathode and anode of the first and second diodes respectively to substantially instantaneously discharge said condensers, whereby two series of voltage variations of saw tooth wave form may be produced, the voltage variations being of opposite polarity and substantially in phase, and means for applying said saw tooth wave form voltage variations to a utilization device.

2. A system for producing voltage variations of saw tooth wave form for deecting a cathode ray beam comprising means for producing a series of positive and a series of negative impulses, a first and a second condenser, means for charging the first of said condensers negatively at a substantially uniform rate, means for charging the second of said condensers positively at a substantially uniform rate, a diode having a cathode and an anode associated with each condenser, means including a resistance for effectively connecting each diode in parallel with its associated condenser, means to apply the produced series of positive impulses to the anode of the diode associated with said first condenser and the produced series of negative impulses to the cathode of the diode associated with said second condenser for substantially instantaneously discharging said condensers, whereby a series of voltage variations of saw tooth wave form and of opposite polarity may be developed across said condensers, and means for applying said voltage variations to the deflecting means of a cathode ray beam.

3. A system for producing two voltage variations of .saw tooth wave form and of opposite polarity for deilecting a cathode ray beam comprising means for simultaneously producing a series of negative and positive impulses of a predetermined frequency, a first and a second condenser, means for' positively charging the first associated 'with the said first and second 'conf densers respectively, whereby voltage variations of saw tooth wave form of opposite polaritymay be developed across said condensers, means for increasing the intensity of the voltage variations,

and means for impressing the increased intensity Voltage variations upon the deiiecting elec-` trodes for a cathode ray beam.

DAVID JOHN FEWINGS. ROLAND JOHN KEMP. 

